Project Summary The main objective of this PPG is to advance our knowledge on the protective mechanisms of antibodies against conserved epitopes of the influenza virus glycoproteins and on optimizing the induction and durability of such antibodies by vaccination using HA-chimeric based immunogens. The knowledge generated by this PPG will advance the development of so called ?universal? influenza virus vaccines against multiple strains and subtypes of influenza viruses. During our previous PPG, we have shown that antibodies directed against specific regions of the HA protein of influenza virus have potent virus neutralizing activities, and play an important role in protection against infection after natural exposure or vaccination. In general, this type of cross-reacting antibodies is present only at low frequencies in immunized individuals, most likely due to the immunodominance of strain specific epitopes. Our collaborators in this PPG, Peter Palese (Project 1), Florian Krammer (Project 4) and Patrick Wilson (Monoclonal Antibody Technology Core) have developed techniques for the generation and identification of these broadly neutralizing antibodies in mice and in humans, including not only those against the conserved HA stem, but also against conserved epitopes in the NA. In order to take advantage of these breakthroughs, we will use the gold-standard animal model of influenza, the ferret, to investigate, in collaboration with Projects 1, 4, and the Technology Core, the potency of the different HA and NA antibodies against different influenza virus strains (Aim 1). Furthermore, to explore vaccination strategies based on HA-based immunogens recognized by broadly neutralizing monoclonal antibodies, we will use the immunogens developed by Project 1 (PI: Palese) and immunization protocols developed by Project 2 (PI: Ahmed) to investigate prime/boost vaccination strategies to generate broad durable protection against influenza A virus challenge in the ferret (Aim 2), and the immune mechanisms (antibodies, T cells) correlating with protection (Aim 3). The information generated by Aims 2 and 3 will provide the basis for potential further development into novel ?universal? influenza vaccine products for humans after completion of this PPG.